Conventionally, a state monitoring apparatus mounted in a vehicle uses a face image obtained by imaging the face of a manipulator in order to monitor the state of the manipulator. For such capturing of a face image, the state monitoring apparatus includes: a light emitting unit for emitting illumination light toward a predetermined area which is preliminarily specified as an area where the face of the manipulator is positioned; and an imaging unit for capturing an image of the face by receiving light incident from the predetermined area.
Patent literature 1 discloses an imaging apparatus that includes: a flash apparatus having a flash related to the above-described light emitting unit; and an imaging element related to the above-described imaging unit. The imaging apparatus provides a length of an exposure period, in which the imaging element is set to an exposure state, to be constant. According to brightness of a subject to be imaged, the apparatus changes the length of a light emission period of the flash in the exposure period, thereby changing a light emission amount. Further, the change of the light emission amount of the flash results in adjusting a light emission start timing of the flash.
In contrast, the above-described state monitoring apparatus, which is different from the imaging apparatus of the patent literature 1, is permitted to change the length of the exposure period in the imaging unit. Consequently, a gradation value of a face image can be adjusted to lie in a pre-specified range regardless of the intensity of environment light reaching the face of the manipulator. The light emitting unit is controlled so as to continue emission of illumination light in the exposure period.